A continuation of research on the catalytic mechanism of phosphoglucomutase is proposed. This will involve a determination of whether there is direct coordination between the bound metal ion and the enzymic phosphate in phosphoenzyme metal-ion complex, and whether this relationship is altered on binding of the substrate or substrate analogs. Whether the binding of substrate or substrate analogs causes a geometrical distortion of the enzymic phosphate of the type that could provide a rationale for the kinetic destabilization of this group also will be investigated. Additional support for operation of an exchange mechanism as opposed to a minimal motion mechanism during the catalytic process also will be sought. An attempt will be made to measure the binding of Li ion to the dephospho-enzyme and is complex with glucose bisphosphate, for comparison with available data on the binding of Li ion to the phospho-enzyme and its complex with glucose 6-phosphate, and the binding of Mg 2 ion to all of these complexes, as a probe of the effect of the metal ion on the thermodynamics of the phosphate transfer that interconverts bound reactants and products. A further investigation of the extent to which conformational changes accompany the catalytic phosphate transfer process and are essential to catalysis also is planned as well as a continuation of work on isolation of phosphoglucomutase in a form which will yield crystals suitable for X-ray diffraction studies.